Modular building block



FIG. 1 is a perspective view, depicting a bottom face in use of a modular building block, facing upward, according to our new design;

FIG. 2 is a front view of the modular building block of FIG. 1;

FIG. 3 is rear view of the modular building block of FIG. 1;

FIG. 4 is a right side view of the modular building block of FIG. 1;

FIG. 5 is a left side view of the modular building block of FIG. 1;

FIG. 6 is a top view of the modular building block of FIG. 1, and depicting the bottom face in use; and,

FIG. 7 is a bottom view of the modular building block of FIG. 1, and depicting the upper face in use.

The features depicted in broken lines form no part of the claimed design. 

CLAIM The ornamental design for a modular building block, as shown and described. 